1. Field of the Invention
The present invention relates to a power supply unit which generates electric power set at a supply voltage. Further, the present invention relates to an electronic control system wherein a microcomputer and electronic circuits controlled by the microcomputer are operated while receiving and consuming the power of the power supply unit.
2. Description of Related Art
An electronic control system with a power supply unit is disposed in a vehicle. The power supply unit receives electric power set at a battery voltage from anon-vehicle battery acting as an external power source and generates electric power set at a supply voltage lower than the battery voltage. In the electronic control system, the unit supplies the electric power of the supply voltage to a microcomputer and electronic circuits including circuits controlled by the microcomputer. As types of the power supply unit, a switching regulator (or a switching power supply unit) and a series regulator (or a series power supply unit) are well known. For example, the switching regulator and the series regulator are disclosed in Published Japanese Patent First Publication No. H02-252007, and the switching regulator is disclosed in Published Japanese Patent First Publication No. 2004-173481.
The switching regulator has transistors connected in series on a current carrying line, a control unit and a smoothing circuit. When electric power of an external power source is supplied to the transistors through the line, the control unit performs an on-off control (or a switching control) for the transistors to supply a required quantity of electric power to the smoothing circuit, and the smoothing circuit outputs electric power set at a constant voltage. Therefore, although the supply voltage of the smoothing circuit cannot be precisely controlled, electric power consumed or lost in the switching regulator is low.
The series regulator has transistors connected in series on a current carrying line and a control unit. The control unit controls the transistors to increase and decrease current outputted through each transistor, so that a voltage difference between terminals of each transistor is precisely controlled. In this case, electric power is consumed in the transistors and is converted into heat. Therefore, although electric power consumed or lost in the switching regulator is large, the supply voltage of the series regulator can be precisely controlled.
To obtain the low loss of electric power in the switching regulator and the precise control in the series regulator, a two-stage power supply unit having both a switching regulator placed in the first stage and a series regulator placed in the second stage has been proposed. In this power supply unit, a switching regulator and a series regulator are disposed in series on a current carrying line connected with an external power source, the switching regulator reduces an input voltage of electric power received from the external voltage to an intermediate voltage slightly higher than a target voltage at a low loss of the electric power, and the series regulator reduces the intermediate voltage of the electric power to the target voltage with high precision.
In this two-stage power control unit, because of a low voltage drop in the series regulator, the loss of the electric power is low in the series regulator. Therefore, electric power set at the target voltage with high precision can be obtained at a low power loss. Especially, the performance of the electronic control system has been heightened year by year, so that electric power required by electronic circuits including a microcomputer has been increased in the system. Therefore, the two-stage power control unit is available for the electronic control system to reduce the loss of the electric power supplied to the electronic circuits while setting the target voltage with high precision.
In a type of electronic control system, a microcomputer performs a standby operation and a wake-up operation. More specifically, when the microcomputer judges that a standby condition is satisfied in the microcomputer, the microcomputer is transferred from a normal operation mode to a standby mode. In this standby mode, the microcomputer merely waits for the satisfaction of a wake-up condition. Therefore, electric power consumed in the microcomputer is low during the standby mode. Then, when the microcomputer detects the satisfaction of a wake-up condition, the microcomputer wakes up and returns to the normal operation mode to be fully operated. Therefore, electric power consumed in the microcomputer becomes large during the normal operation mode.
Especially, in an electronic control system disposed in a vehicle, even when the engine is stopped (more specifically, a power source of a vehicle ignition system is set in an off state) so as not to charge electric power to a non-vehicle battery, some electronic circuits are sometimes or intermittently operated. To reduce electric power consumed in a microcomputer for controlling the electronic circuits, only when the operation of the electronic circuits is required, the microcomputer is woken up and controls the electronic circuits.
Further, in the switching regulator, when transistors acting as switching elements are frequently turned on and off in the switching operation under control of a driving control unit, electric power consumed in the driving control unit for the switching operation is comparatively large. When electronic circuits consuming electric power of a power supply unit during the normal operation mode are set in the standby mode, none of the electronic circuits require the electric power. To reduce dark current consumed in the whole electronic control system when the electronic circuits are set in the standby mode, it is effective that the switching control for the transistors is stopped to stop the operation of the switching regulator.
A conventional electronic control system with a two-stage power control unit is described with reference to FIG. 1 and FIG. 2. In this system, when a microcomputer for controlling a switching regulator is set in a standby mode, the operation of the switching regulator is stopped.
FIG. 1 is a circuit view of an electronic control system with a two-stage power control unit in the prior art, while FIG. 2 is an explanatory view of the operation of the system shown in FIG. 1.
As shown in FIG. 1, an electronic control system has a two-stage power control unit 110 and a microcomputer 120. The unit 110 reduces an input voltage V1 (e.g., approximately 12V) applied by an on-board battery (not shown) to a supply voltage V3 (e.g., 5V) and supplies the electric power of the supply voltage V3 to the microcomputer 120 and peripheral circuits controlled by the microcomputer 120.
The unit 110 has a voltage drop type switching regulator 100 and a first series regulator 130 disposed in series. The unit 110 further has a second series regulator 140 disposed parallel to the regulators 100 and 130. The switching regulator 100 reduces the input voltage V1 to an intermediate voltage V2 equal to 6V lower than the voltage V1 and higher than the supply voltage V3. The series regulator 130 reduces the voltage V2 to the supply voltage V3.
The switching regulator 100 has an n-channel type MOSFET (metal oxide semiconductor field effect transistor) 101 of which the drain is connected with a power receiving line La through which electric current of the input voltage V1 is supplied to the FET 101, a smoothing circuit 102 connected with the source of the FET 101, and a driving control circuit 104 connected with the gate of the FET 101. The FET 101 performs a switching operation under control of the circuit 104. The smoothing circuit 102 smoothes the voltage of electric current outputted from the FET 101. The circuit 104 controls the FET 101 under control of the microcomputer 120 to adjust the smoothed voltage of the circuit 102 to the intermediate voltage V2.
The smoothing circuit 102 has a coil L102 of which terminals are, respectively, connected with the source of the PET 101 and a connection line Lb, a capacitor C102 of which terminals are, respectively, connected with the connection line Lb and a ground line, and a flywheel diode D102 of which terminals are, respectively, connected with the source of the FET 101 and another ground line. The coil L102 and the capacitor C102 act as a low pass filter to smooth the voltage of the current outputted from the PET 101. The flywheel diode D102 protects the FET 101 from the back electromotive energy generated in the coil L102 when the FET 101 is turned off. That is, when the FET 101 is turned off, a circulating current flow through the diode D102 to discharge electric power which is accumulated in the coil L102 during the on-state of the FET 101. Therefore, the regulator 100 outputs the smoothed voltage equal to the intermediate voltage V2 to the connection line Lb.
The first series regulator 130 has an output transistor (or a p-n-p bipolar transistor) 131 having the emitter connected with the connection line Lb and the collector connected with a power supply line Lc, a driving control circuit 132 connected with the base of the transistor 131, and a capacitor C133 of which terminals are, respectively, connected with the supply line Lc and a ground line. The circuit 132 linearly drives the transistor 131 in response to an instruction of the microcomputer 120 and controls the transistor 131 to adjust the supply voltage V3 of the transistor 131 to a target value of SV. The capacitor C133 stabilizes the supply voltage V3 applied to the supply line Lc. Therefore, the regulator 130 reduces the intermediate voltage V2 of the regulator 100 to the supply voltage V3 and supplies electric power of the supply voltage V3 to electronic circuits including the microcomputer 120 and peripheral circuits controlled by the microcomputer 120 through the supply line Lc.
The second series regulator 140 has an output transistor (in this embodiment, a p-n-p bipolar transistor) 141 having the emitter connected with the line La and the collector connected with the supply line Lc, a driving control circuit 142 connected with the base of the transistor 141, and a capacitor C143 of which terminals are, respectively, connected with the supply line Lc and a ground line. The circuit 142 linearly drives the transistor 141 and controls the transistor 141 to adjust the supply voltage V3 of the transistor 141 to the target value of 5V. The capacitor C143 stabilizes the supply voltage V3 applied to the supply line Lc. Therefore, the regulator 140 reduces the input voltage V1 of the line La to the supply voltage V3 and supplies electric power of the supply voltage V3 to the electronic circuits.
The second series regulator 140 is always operated to produce electric current of the supply voltage V3 from electric current of the voltage V1. In contrast, the regulators 100 and 130 are operated only when the microcomputer 120 instructs the regulators 100 and 130. The electric current outputted from the regulator 140 is set to be lower than that outputted from the regulator 130. More specifically, the base current outputted from the circuit 142 to the transistor 141 is set to be lower than that outputted from the circuit 132 to the transistor 131. Therefore, even when no current is outputted from the regulators 100 and 130 to the electronic circuits, the regulator 140 supplies electric current to the electronic circuits.
As shown in FIG. 2, when the microcomputer 120 judges that a standby condition of the control system is satisfied, the mode of the microcomputer 120 is transferred from the normal operation mode to the standby mode, and the microcomputer 120 changes the level of an instruction signal from the high level to the low level. During the standby mode of the microcomputer 120, the microcomputer 120 operates only a wake-up condition detecting circuit (not shown) among various circuits of the microcomputer 120 to detect the satisfaction of a wake-up condition, so that the electric power consumed in the microcomputer 120 is reduced.
In response to the instruction signal set to the low level, the regulators 100 and 130 are set in the stop state together More specifically, the circuit 104 stops the switching control for the FET 101 and locks the FET 101 to the off state, and the circuit 132 stops the linearly-driving control for the transistor 131 and locks the transistor 131 to the off state. That is, the microcomputer 120 stops operations of the regulators 100 and 130. During the standby state of the regulator 100, electric charge accumulated in the capacitor C102 is discharged, so that the capacitor C102 has no charge.
During the standby mode of the microcomputer 120, the electronic circuits including the microcomputer 120 receive the minimum quantity of electric power required in the electronic circuits only from the regulator 140. Therefore, electric power consumed in the electronic circuits is reduced during the standby mode.
Thereafter, when the microcomputer 120 receives a specific signal indicating a wake-up condition, the wake-up condition detecting circuit of the microcomputer 120 detects that a wake-up condition is satisfied. In response to this detection, the microcomputer 120 changes the instruction signal to the high level without changing its own mode and outputs this instruction signal to the circuits 104 and 132 of the regulators 100 and 130. In response to the instruction signal being changed to the high level, the regulator 100 is set to the start-up state, while the regulator 100 is still set in the stop state. More specifically, the circuit 104 immediately restarts the switching control for the FET 101. In this case, because of no electric charge accumulated in the capacitor C102 during the standby mode, after the restart of the switching control for the FET 101, the voltage of the connection line Lb depending on the electric charge of the capacitor C102 is too low for a period of time Ta to adjust the connection line Lb to the intermediate voltage V2. In other words, after the instruction signal being changed to the high level is received, it takes the period of time Ta until the voltage of the connection line Lb is increased to the intermediate voltage equal to 6V. Then, the regulator 100 is set to the normal operation state in response to an elapse of the period of time Ta.
To reliably operate the regulator 130, the circuit 132 of the regulator 130 waits for the period of time Ta after a reception of the instruction signal changed to the high level, and then the circuit 132 is set to the start-up state. That is, the circuit 132 starts driving the transistor 131 in response to an elapse of the period of time Ta. When a certain period of time Tb (Tb>Ta) has elapsed after the reception of the instruction signal changed to the high level, the regulator 130 is set to the normal operation state to reliably output the supply voltage V3 of the target value to the electronic circuits including the microcomputer 120. Because the microcomputer 120 can fully become operated while consuming electric power of the supply voltage V3, the microcomputer 120 changes its own mode to the normal operation mode in response to an elapse of the period of time Tb starting from the output of the instruction signal changed to the high level.
After the transistor 131 receives the intermediate voltage V2 equal to the intermediate value of 6V, the regulator 130 requires a period of time Tb−Ta equal to the difference between the period of time Tb and the period of time Ta to sufficiently supply the electric current of the supply voltage V3 to the electronic circuits. That is, after the transistor 131 receiving the intermediate voltage V2 starts performing the driving operation, it takes the period of time Tb−Ta until the regulator 130 stably outputs the supply voltage V3.
Assuming that the circuit 132 immediately performs the linearly-driving control for the transistor 131 just after the reception of the instruction signal changed to the high level, the regulator 130 cannot output electric current of the supply voltage V3 to the supply line Lc just after the reception of the instruction signal or an elapse of the period of time Ta. Assuming that the microcomputer 120 changes its own mode to the normal operation mode before an elapse of the period of time Tb, a large quantity of electric current required by the electronic circuits immediately flows from the regulator 130 to the electronic circuits including the microcomputer 120 set to the normal operation mode. In this case, the voltage of electric current outputted from the regulator 140 is lowered, so that the microcomputer 120 cannot reliably perform its normal operation.
Therefore, the mode of the microcomputer 120 is transferred to the normal operation mode when the period of time Tb has elapsed after the change of the instruction signal to the high level.
As described above, in the conventional electronic control system, during the standby mode of the microcomputer 120, the regulator 100 locks the FET 101 to the off state, and none of the capacitors C102 and C133 accumulate electric charge. When the microcomputer 120 is woken up, it is impossible for the regulators 100 and 130 to supply electric current of the supply voltage V3 to the electronic circuits including the microcomputer 120 in a short time. Therefore, it is undesirably required that the transfer from the standby mode to the normal operation mode in the microcomputer 120 is largely delayed. That is, it is difficult for the electronic circuits including the microcomputer 120 set in the standby mode to wake up and perform their normal operations in a short time.